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Using selective media containing galactitol, over 130 Enterobacteriaceae have been isolated from paper mill process waters collected from different localities. These bacteria were extensively characterized and tested for acetylene-reducing (nitrogen-fixing) activity under anaerobic conditions. High activity was found in representatives of Klebsiella pneumoniae, Enterobacter aerogenes, Enterobacter cloacae, Erwinia herbicola, Citrobacter freundii, Citrobacter intermedius, and Escherichia coli. Under argon, nitrogenase synthesis was generally not repressed by 5 mM l-glutamate, l-aspartate, l-leucine or Casamino Acids (0.5 g/liter). In many strains, both the specific activities (nanomoles of C(2)H(4) per minute per milligram of protein) and the activities (nanomoles of C(2)H(4) per minute) had considerably declined after 24 h. In three selected strains, activity in intact cells grown under nitrogen was unaffected by the presence during assay of 10 mM l-amino acids or ammonium acetate. All of the strains examined were tolerant towards inactivation of nitrogen-fixing activity by 1.8% (vol/vol) oxygen during assay, and inactivation by up to 10% oxygen was partly reversible. Representatives of the six taxa synthesized nitrogenase in stirred aerobic cultures, though the protein concentrations attained were lower than under anaerobic conditions. It seems reasonable to suggest that under natural conditions, nitrogen fixation is able to contribute significantly to the nitrogen economy of the cells.  相似文献   

3.
Aquaspirillum magnetotacticum strain MS-1 and two nonmagnetic mutants derived from it reduced C2H2 microaerobically but not anaerobically even with NO3 ?. This organism apparently is not capable of NO3 ?-dependent nitrogen fixation. Cells ofA. magnetotacticum reduced C2H2 at rates comparable to those ofAzospirillum lipoferum grown under similar conditions, but much lower than that ofAzotobacter vinelandii grown aerobically. Cells ofA. magnetotacticum in anaerobic cultures lacking NO3 ? did not reduce C2H2 until O2 was introduced. Optimum rates of C2H2 reduction byA. magnetotacticum were obtained at 200 Pa O2. C2H2 reduction was inhibited by more than 1 kPa O2 or 0.2 mM NO3 ? or NH4 +. These results suggest thatA. magnetotacticum fixes N2 only under microaerobic, N-limited conditions.  相似文献   

4.
Summary Acacia greggi, Cercidium floridium, and Olneya tesota seeds were inoculated with soil from beneath mature native desert trees and grown in the greenhouse on a nitrogen free media. Olneya tesota seedlings nodulated and reduced acetylene to ethylene. Nodulation or acetylene reduction was not observed in A. greggi or C. floridium. This is the first report of nodulation and nitrogen fixation in Olneya tesota.  相似文献   

5.
Sorghum and corn breeding lines were grown in soil in field and greenhouse experiments with and without an inoculum of N2-fixing in Spirillum strains from Brazil. Estimated rates of N2 fixation associated with field-grown corn and sorghum plants were less than 4 g of N2/ha per day. The mean estimated N2-fixation rates determined on segments of roots from corn inoculated with Spirillum and grown in the greenhouse at 24 to 27 degrees C were 15 g of N2/ha per day (16 inbreds), 25 g of N2/ha per day (six hybrids), and 165 g of N2/ha per day for one hybird which was heavily inoculated. The corresponding mean rates determined from measurements of in situ cultures of the same series of corn plants (i.e., 16 inbreds, six hybrids, and one heavily inoculated hybrid) were 0.4, 2.3, and 1.1 g of N2/ha per day, respectively. Lower rates of C2H2 reduction were associated with control corn cultures which had been treated with autoclaved Spirillum than with cultures inoculated with live Spirillum. No C2H2 reduction was detected in plant cultures treated with ammonium nitrate. Numbers of nitrogen-fixing bacteria on excised roots of corn plants increased an average of about 30-fold during an overnight preincubation period, and as a result acetylene reduction assays of root samples after preincubation failed to serve as a valid basis for estimating N2 fixation by corn in pot cultures. Plants grown without added nitrogen either with or without inoculum exhibited severe symptoms of nitrogen deficiency and in most cases produced significantly less dry weight than those supplied with fixed nitrogen. Although substantial rates of C2H2 reduction by excised corn roots were observed after preincubation under limited oxygen, the yield and nitrogen content of inoculated plants and the C2H2-reduction rates by inoculated pot cultures of corn, in situ, provided no evidence of appreciable N2 fixation.  相似文献   

6.
Nitrogen fixation (acetylene reduction) on a coral reef   总被引:2,自引:1,他引:2  
Nitrogen fixation rates associated with various substrates on a fringing reef at Eilat, Red Sea, were estimated by in situ acetylene reduction. High rates of acctylene reduction were associated with bare substrates, such as sand and dead coral skeletons. Low rates of acetylene reduction were associated with substrates covered by macroalgae or living coral tissue. Estimates of nitrogen fixation in various reef zones, based on these measurements, indicate that the sand-covered lagoon is responsible for more than 70% of the fixation in the reef. Consequently, the lagoon may serve as an important source of nitrogen for the coral reef community.  相似文献   

7.
The effect of size of structural aggregates on the intensity of nitrification and nitrogenase (nitrogen: acetylene oxidoreductase) activity was investigated in three soils. In two of them the nitrogenase activity was limited by addition of glucose. Aggregates of a larger diameter (2-4 mm) exhibited a considerably higher nitrogenase activity than those with a diameter smaller than 2 mm. This effect was even more pronounced when the soil samples were repeatedly intensively aerated. On the contrary, smaller aggregates (0.5-2 mm) exhibited more intensive nitrification.  相似文献   

8.
The involvement of epiphytic microorganisms in nitrogen fixation was investigated in a shallow freshwater pond near Ithaca, N.Y. The acetylene reduction technique was used to follow diel and seasonal cycles of nitrogen fixation by epiphytes of Myriophyllum spicatum. Acetylene-reducing activity was maximal between noon and 6 p.m., but substantial levels of activity relative to daytime rates continued through the night. Experiments with the seasonal course of activity showed a gradual decline during the autumn months and no activity in January or February. Activity commenced in May, with an abrupt increase to levels between 0.45 and 0.95 nmol of ethylene formed per mg (dry weight) of plant per h. Through most of the summer months, mean rates of acetylene reduction remained between 0.15 and 0.60 nmol/mg (dry weight) per h. It was calculated from diel and seasonal cycles that, in the pond areas studied, epiphytes were capable of adding from 7.5 to 12.5 μg of N per mg of plant per year to the pond. This amount is significant relative to the total amount of nitrogen incorporated into the plant. Blue-green algae (cyanobacteria), particularly Gloeotrichia, appeared to bear prime responsibility for nitrogen fixation, but photosynthetic bacteria of the genus Rhodopseudomonas were isolated from M. spicatum and shown to support high rates of acetylene reduction.  相似文献   

9.
Summary Acetylene reduction to ethylene by filtrates of rumen contents has been studied. The Km values for acetylene are comparable to those reported for nitrogenase enzymes from N2 fixing bacteria. The enhancement of ethylene production from acetylene by phosphate and pyruvate suggests that the reduction was carried out by anaerobic microorganisms. Acetylene reduction occurred in the rumen only when a high nitrogen diet was fed to the sheep. Some microorganisms isolated from the rumen contents were grown anaerobically under N2 gas on agar not supplemented with combined nitrogen. Methane production by filtrates of rumen contents was found to be inhibited by acetylene.  相似文献   

10.
InPisum sativum cultivated under standard growth conditions the extent of N2 fixation with time estimated by the acetylene reduction assay (PN2F) and rates of the actual nitrogen accumulation of plant biomass (ANA) were calculated from six independent growth experiments. In the plants inoculated with indigenous soilRhizobium populations and cultivated on 0.63 mmol/L nitrate level the percentage PN2F:ANA ratios ranged from 25.7 to 61.5%. In peas inoculated with the inoculant strain the PN2F:ANA ratios were markedly higher, ranging from 59.8 to 65.1%. The plants cultivated on N-free nutrient solutions showed both PN2F:ANA and C2H4N2 ratios to be somewhat higher compared with the 0.63 mmol/L nitrate cultivated plants.  相似文献   

11.
The leguminous tree mesquite (Prosopis spp) exists on millions of hectares of semi-arid regions of the world. No whole plant acetylene reductions for mesquite have been reported in the literature and nodulation has only been reported for three of the forty-four species. We report greenhouse studies in which 12Prosopis species representing African and North and South American germplasm (1) became nodulated when inoculated with rhizobia strain isolated from a North American mesquite, (2) grew on a nitrogen free nutrient media, (3) reduced acetylene to ethylene, and (4) had a positive significant correlation between the acetylene reduction rates and above ground dry matter. The capability of mesquite to fix nitrogen must now be considered firmly established.  相似文献   

12.
13.
Acetylene reduction by nitrogen-fixing blue-green algae   总被引:23,自引:0,他引:23  
Summary Known nitrogen-fixing species of blue-green algae are capable of reducing acetylene to ethylene, but acetylene is not reduced by Anacystis nidulans, which does not fix nitrogen. Cycad root nodules which contain blue-green algae as endophytes reduce acetylene. Acetylene reduction is inhibited by carbon monoxide. Nitrate or ammonium-nitrogen has no immediate effect on algae reducing acetylene, but algae grown on nitrate-nitrogen gradually lose their capacity to reduce acetylene. Nitrate-nitrogen also inhibits heterocyst formation in these algae and there is a fairly direct correlation between the abundance of heterocysts in a particular sample and its capacity to reduce acetylene. Aphanizomenon flosaquae reduces acetylene and fixes nitrogen in unialgal culture and there is strong presumptive evidence that these reductions are carried out by the alga rather than by associated bacteria. The molar ratios of ethylene: ammonia produced vary within the range 1.4–1.8.  相似文献   

14.
15.
Summary A method for intensively sampling soil for nitrogen fixation potential using acetylene reduction assay is discussed. Acetylene was generated from calcium carbide. Soil cores were incubated in Mason jars with specially adapted lids. Air samples from the jars were stored and transported over dry KOH in 10 ml serum vials. The method overcomes many problems associated with other sampling procedures, and produces statistically reproducible data.Contribution #4 — Devon Island IBP Project and CCIBP contribution #173.Contribution #4 — Devon Island IBP Project and CCIBP contribution #173.  相似文献   

16.
Summary Soil properties of pioneer Pinus flexilis stands with similar topography and climate were investigated. Soils supporting this tree in association with Cercocarpus ledifolius were found to have higher percentages of total nitrogen than soils beneath similar stands lacking Cercocarpus.An excavated Cercocarpus ledifolius shrub in a Pinus flexilis stand in the San Bernardino Mountains of California was found to be nodulated and these nodules were found to be capable of fixing nitrogen. Other known nitrogen-fixing shrubs are frequent associates of Pinus flexilis in extreme sites.Implications of the phylogenetic relationship of some nitrogen-fixing species are briefly discussed, as well as their frequent occurrence in pioneer or extreme habitats.  相似文献   

17.
Root segments and root-soil cores (6.5-cm diameter) from fields and nurseries of winter wheat and sorghum were tested for N2 fixation by using the acetylene reduction assay. Wheat samples (approximately 1,200) from 109 sites generally had low or no activity (0 to 3.1 nmol of C2H4 produced per h per g [dry weight] of root segments), even after 24 h of incubation. However, a commercial field of Scout 66, located in western Nebraska, exhibited appreciable activity (290 nmol of C2H4 produced per h per g [dry weight] of root segments). Of 400 sorghum lines and crosses, grain sorghums (i.e., CK-60A, Wheatland A, B517, and NP-16) generally exhibited higher nitrogenase activity than forage sorghums or winter wheats. CK-60A, a male sterile grain sorghum, was sampled at four locations and had the most consistent activity of 24 to 1,100 nmol of C2H4 produced per h per core. The maximum rate extrapolated to 2.5 g of N per hectare per day. Numerous N2-fixing bacterial isolates were obtained from wheat and sorghum roots that exhibited high nitrogenase activity. Most isolates were members of the Enterobacteriacae, i.e., Klebsiella pneumoniae, Enterobacter cloacae, and Erwinia herbicola.  相似文献   

18.
Clustering of nitrogen fixation (nif) genes in Rhizobium meliloti.   总被引:13,自引:18,他引:13  
  相似文献   

19.
Acetylene reduction by pure cultures of Rhizobia.   总被引:13,自引:8,他引:13  
Acetylene reduction has been demonstrated in pure cultures of rhizobia. The requirements and conditions necessary for the activity in Rhizobium sp. 32H1 are described. The most important factors are a low cell density and a very low oxygen concentration.  相似文献   

20.
Nitrogen fixation was measured in four subarctic streams substantially modified by beaver (Castor canadensis) in Quebec. Acetylene-ethylene (C2H2 C2H4) reduction techniques were used during the 1982 ice-free period (May–October) to estimate nitrogen fixation by microorganisms colonizing wood and sediment. Mean seasonal fixation rates were low and patchy, ranging from zero to 2.3 × 10–3 µmol C2H4 · cm–2 · h–1 for wood, and from zero to 7.0 × 10–3 µmol C2H4 · g AFDM–1 · h–1 for sediment; 77% of all wood and 63% of all sediment measurements showed no C2H2 reduction. Nonparametric statistical tests were unable to show a significant difference (p > 0.05) in C2H2 reduction rates between or within sites for wood species or by sediment depth.Nitrogen contributed by microorganisms colonizing wood in riffles of beaver influenced watersheds was small (e.g., 0.207 g N · m–2 · y–1) but greater than that for wood in beaver ponds (e.g., 0.008 g N · m–2 · y–1) or for streams without beaver (e.g., 0.003 g N · m–2 · y–1). Although mass specific nitrogen fixation rates did not change significantly as beaver transform riffles into ponds, the nitrogen fixed by organisms colonizing sediment in pond areas (e.g., 5.1 g N · m–2 · y–1) was greater than that in riffles (e.g., 0.42 g N · m–2 · y–1). The annual nitrogen contribution is proportional to the amount of sediment available for microbial colonization. We estimate that total nitrogen accumulation in sediment, per unit area, is enhanced 9 to 44 fold by beaver damming a section of stream.  相似文献   

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